A positive type photosensitive resinous composition has been widely used in the manufacturing process of semi-conductor devices, printed circuit boards, printing plates and the like.
Most popular positive type photosensitive resinous composition comprises an alkali soluble novolak resin added with a quinone diazide compound.
Since the quinone diazide compound is soluble in an organic solvent but insoluble in water, the formed resinous coating is hardly soluble in an aqueous alkaline developer.
However, when the coating is exposed to UV rays, the exposed quinone diazide group is decomposed, being changed to ketene and then to carboxylic groups.
Therefore, the exposed area may be converted to a soluble nature, and such decomposition is ingeniously utilized in that system.
As for positive type photosensitive materials typical examples are 1,2-quinone diazide compounds described in, for example, "Light-sensitive Systems" J. Kosar, John Wiley and Sons Inc. 339-357, and various patents and publications.
Such positive type photosensitive composition is, in general, far more excellent in resolving power than those of negative type photosensitive resinous compositions and hence is widely used as an etching resist in the preparation of printed circuits boards, integrated circuit and the like.
However, since the base material is a novolac resin prepared by a polycondensation, there is a wide fluctuation in the properties of the resin product and since the softening point is considerably high despite of the comparatively lower molecular weight of the resin, there is the drawback of excessive brittleness in respect to the resist film prepared. Furthermore, since the adhesion to the base plate is not good, it is still desired to increase the adhesion properties.
There is an another approach wherein a 1,2-quinone diazide compound is admixed with an acrylic resin which is a copolymer of a conjugated diolefinic hydrocarbon a, monoolefinic unsaturated compound and an .alpha.,.beta.-ethylenically unsaturated carboxylic acid, as disclosed in Japanese Patent Publication (unexamined) 122031/81.
This system may impart the desired flexibility to the resist film, therefore resulting in excellent adhesion between the base plate and the formed resist film.
However, in order to give the desired alkali solubility to the exposed resist film, it is essential that the content of .alpha.,.beta.-ethylenically unsaturated carboxylic acid in said acrylic resin should be as high as possible, which, in turn, will cause the undesired swelling of the unexposed image area in the developing stage, resulting in poor resolving power.
The inventors have previously proposed, under the circumstances, positive type photosensitive resinous compositions which are excellent in flexibility and adhesion of the formed resist film and extremely low in swelling of the unexposed resist at the time of development (as, for example, Japanese Patent Publication (unexamined) 189857/88, ibid 281153/88, ibid 281154/88).
However, despite of such proposals, there is an undesired decrease in the film properties under severe conditions.
Especially, in the case of using such composition as an etching resist for the preparation of printed circuit boards with an electrolytically copper-plated board, the etching time in the actual production line is usually set in a range of 1.1 to 1.5 times the required etching time to remove the undesired copper, paying due consideration of fluctuation in the plating thickness in the base plate and between the respective base plates.
Therefore, as an etching resist film, a far better adhesion to the copper surface is usually required.
Nevertheless, the proposed resinous compositions cannot give a fully satisfying answer to this problem.
In order to improve the adhesion of photosensitive resinous compositions toward metals and the like, various proposals for making use of phosphoric ester compounds have been made.
For example, in Japanese Patent Publication No. 27457/76, there is mentioned a composition comprising, as essential components, an ester of phosphoric acid with a hydroxyl of polymerizable monomer, vinyl monomers and particular urethane modified oilfree alkyd resin; in Japanese Patent Publication (unexamined) No. 99202/81, a photo-curing type composition containing a particular phosphoric acid component and having improved adhesion properties to the metal substrate; and in Japanese Patent Publication (unexamined) No. 10668/82, a photo-curing type adhesive composition, based on a low molecular weight acrylic copolymer containing a specified amount of a particular organic phosphoric acid ester monomer.
Other compositions containing phosphoric acid ester compounds having polymerizable unsaturated bonds are stated in Japanese Patent Publication (unexamined) Nos. 67751/78; 17569/82; 18263/83; 208313/85; 32044/87; 92618/88 and the like.
The phosphoric acid ester compounds used in these techniques are characterized in that at least one free phosphoric acid group is necessarily contained in the molecule of said compound.
It is understood that due to its higher polarity and large dissociation constant alone or to its synergism with the particular type of combined materials, adhesion toward metals or other substrates must be increased.
It is, therefore, easily thought of by those skilled in the art, to make use of the abovementioned technique in a positive type photosensitive resinous composition.
In fact, in Japanese Patent Publication, (unexamined) Nos. 206293/86, 189857/88 and 281153/88, all filed by Nippon Paint Co. Ltd, such phosphoric acid ester groups have been incorporated into acrylic resins by effecting copolymerization of phosphoric acid ester compounds having polymerizable unsaturation bonds and other copolymerizable acrylic monomers.
However, in the case of positive type photosensitive resinous compositions, the unexposed area (the so-called pattern area desired) must be resistant toward alkaline developers and should not be dissolved or swollen in the developer, while the exposed area (the so-called undesired portion) is dissolved and removed off by the alkaline developer.
However, if the phosphoric acid compound is introduced in the resin in a sufficient quantity required to improve the adhesion to the metal, the alkaline resistance at the unexposed area will inevitably be lowered due to the alkaline affinity of the phosphoric acid groups, and there always occurs, at the time of development, undesired swelling of the unexposed area or undesired solution problems.
Thus, there occurs new troublesome questions that the solubility difference between the unexposed and exposed areas will become very small.
It is, therefore, an object of the invention to provide a positive type photosensitive ,resinous composition which is excellent in adhesion toward metals and whose coating is extremely resistant to swelling, at the unexposed area, in an alkaline developer and which is specifically useful as a resist film.